RS232 connection problems

[Bruce Juntti]

I bought the NMIY0031 a couple of years ago and I'm just now hooking the thing up. I made my own cable as follows:<p>Laptop DB9NIMY0031 Header Pin<br>------------------------------------<br>TD (3)5 (MAX232 Pin 8)<br>RD (2)3 (MAX232 Pin 7)<br>SG (5) 9 (GND)<p>Well, it doesn't work. I hooked up a scope to the MAX232 and I see my keystrokes going in, but when I reset the board, I don't see the monitor banner message. Does the PC need other pins (e.g. CTS/RTS) wired to see data?<br>I'm also seeing a strange logic level on the scope on SI (MAX232 pin 7) - it seems to be varying +/- 12 volts instead of between ground and -12 volts. Could I have a bad cap on the MAX232? I sure would appreciate any suggestions - I seem to cursed when it comes to getting any microprocessor boards working.<p>Bruce<br>

[kmcnicho]

It's been a while since your post. Did you get the board working ?<p>Everything looks fine on your cable. A PC serial port should not require RTS/CTS. Also, the logic level for RS-232 is +/- 3V to 30V(I always forget the upper limit, so it might not be 30V).<p>Are you using the maxterm program supplied by new micros ? Did you see data coming across the RD line when the board is reset ?

[Bruce Juntti]

Thanks for the answer on the RS232. I got it working! The problem was a loose ground pin on the DB9 on the laptop side. I could see data on my 'scope when I reset the board and data into it when I tapped the keys on the lapslab. It was driving me up a wall! But, after disconnecting the other leads (CTS, etc.), I found that you are indeed correct about not needing those leads. I do appreciate the help very much, though!

[kmcnicho]

you're welcome. In the future if you're using a host that requires RTS/CTS with a similar board you can wire RTS to CTS, and CD on the host, so it thinks it's always ok to send. It's basically a null modem cable then, but without the TD/RD wires switched.<p>